The scale on a map is 1cm : 1km. If two cities are 2cm apart on the map, what is the actual distance in km between the two cities?
Answer: The scale means that every 1cm on the map corresponds to an actual distance of 1km. A distance of 2cm on the map is the same as 2 $\cdot$ 1cm. The actual distance between the two cities is 2 $\cdot$ 1km, or 2km.